Influence of the magnetic field sweep rate on flux creep in highly textured thin film of YBa2Cu3O7-δ

We investigated the influence of the field sweep rate on the magnetic relaxation and the critical current density of a highly textured thin films of YBa2Cu3O7-δ at different temperatures and fields parallel to the c-axis. We find that the actual M versus ln t relationship can be deduced experimentally by a transformation of the form t→t+τ+τvs in which τ is a transient time proportional to R x (dH/dt)-1, τvs the time constant of the magnetometer (∝0.25 s) and R the effective radius of the superconducting film averaged along the a-b planes. As a result, all the relaxation curves collapse into a single-master one that is independent of the experimental conditions. The parameter τ obeys approximately the relationship τ x dH/dt∼2 Oe in the range T<30 K and depends on the film thickness. The resulting J versus ln t relationship deviates from linearity for all the explored temperatures and fields. (orig.)